In one example of a conventional multipipet, a plurality of plungers are fixedly attached to a common supporting body at a predetermined pitch and a plurality of cylinders are also fixedly attached to another common supporting body at a predetermined pitch. In operation, the plungers are simultaneously and fittingly advanced in the respective cylinders against the force of springs. The plungers are then returned to suck predetermined amounts of liquid into the cylinders and then moved downward again to discharge the predetermined amounts of liquid from the cylinders.
The above-described arrangement suffers, however, from the following disadvantages. Since the pitch of the plungers and that of the cylinders are fixed, if there is any difference between the pitch of the plungers and that of the cylinders, this pitch error cannot be tolerated and the plungers are likely to be rubbed locally against the side walls of the cylinders to an extent corresponding to the degree of the dimensional error. In such a case, the reciprocating motion of the plungers cannot be effected smoothly, which interferes with the operation and lowers the pipetting accuracy. This problem may be overcome by increasing the precision of assembly, but this would lead to a very high cost for assembling the multipipet.
According to another prior art (see for example, Japanese Patent Publication No. 35557/1977), a plurality of plungers are oscillatably attached to a common supporting body through respective springs so that any small pitch error between the plungers and the cylinders is absorbed by each individual plunger which oscillates in such a manner as to adjustably fit the corresponding cylinder, thereby enabling the plungers to reciprocate smoothly within the cylinders, and thus eliminating the above-described disadvantages.
However, the above-described prior art suffers from the following disadvantages since the cylinders are still fixedly attached to another common supporting body. More specifically, when the distal end portions of the cylinders of the multipipet are simultaneously and respectively inserted into a plurality of nozzle tips supported on a nozzle tip rack, if there is an error between the pitch of the cylinders and that of the nozzle tips, some of the nozzle tips cannot be tightly fitted onto the distal end portions of the corresponding cylinders. Accordingly, it is necessary to make a manual check to determine whether or not each individual nozzle tip has been tightly and properly fitted onto the corresponding cylinder and, if any nozzle tip has not been properly fitted, it must be manually forced so as to fit onto the cylinder in its proper position. Thus, the operation of this prior art has been troublesome.